Morwenna, Tillyrose and Surfermum ..... I too am a "second" and I sympathise 150% with what you're going through. I am going through very similar problems and far from getting on with her life, my partner's (of 5 years) ex-wife seems to become increasingly bitter as time goes on.
My DP hasn't seen 1 of his children for 9 months. The so-called "mother" encorages this and does nothing to facilitate contact whatsoever. He is heartbroken - she is gloating. Yet of course, her deliberate obstruction (we have loads of written evidence of her lack of caring and refusal to help remedy the situation) makes no difference to her holding out her hand for money for the "absent" child every month.
The children are perpetually told lies about their dad .... this emotional abuse is reflected in their behaviour in so many ways, yet her desire to score points against her ex is far more important than the children's well being.
I could go on .... and on ... and on .... with a 101 stories about obstruction, lies, using children as weapons, wasting money we absolutely cannot afford through her spite, children being sent with no clothes, her moving 140 miles away from where children were born but never sharing an inch of the driving, her insulting me on a regular basis .... but I don't have the time.
What I don't get is why it has to be like this at all ? I met DP 2+ years after they split ... but it would seem he is not supposed to move on, even though she has had umpteen boyfriends since.
I am a "first" too and I know damn well that I have played fair by my son. I never badmouth his dad to him, never obstruct contact (in fact I encourage it) and consequently, our son is well adjusted and happy which is all that should matter - no matter what I think of his dad.
What has been my absolute lifeline as a second wife is a site called "The British Second Wives Club". I've been a member for over a year and it's my sanctuary. There are 100s of members, all with similar stories who support and advise each other. No-one judges you, no-one disbelieves you, you are not "branded" (as you often are in public) as a "home-wrecker" and nor does anyone expect you to have to put up and shut up with totally damaging anti-social behaviour just because your ex was once married to someone who turned out to be a spiteful bitter bitch.
There are several forums covering the spectrum of problems 2nd wives & partners often face if they are unlucky enough to have a mad ex-wife. It really has helped me to unload hugely, because, often our husbands and partners feel their loyalties torn between doing what's right for their 1st children (but this is open to such terrible abuse and emotional blackmail by an ex-wife if she is the greedy sort) and their new family.
I'd really recommend anyone in our situation to have a look:
British Second Wives Club
Click "join" at the top of the page on this link which will tell you more about the club.